Molded lens having an outer circumference and first and second optical surfaces with cut off peripheral portions, and molding die for the molded lens

ABSTRACT

A molded lens used in an optical pickup device provided with a plane of incidence having a first optical surface and a plane of emergence having a second optical surface, and a form of an outer circumference of the molded lens is formed by a first straight line portion which is in parallel substantially with a plane including an optical axis, a second straight line portion which is in parallel with the first straight line portion and is symmetric with the first straight line portion about the plane and by two circular arcs each connecting end portions of the first and second straight line portions. A part of a fringe of each of the first and second optical surfaces is substantially in a form of a circle whose center is on the optical axis is cut off by each of the first and second straight line portions.

BACKGROUND OF THE INVENTION

The present invention relates to a molded lens used in an optical pickupdevice and to a molding die for the molded lens.

An optical pickup device used for recording and reproducing ofinformation employing an optical information recording medium (anoptical disc) is constructed by combining various types of opticalelements such as an objective lens, a collimator, a coupling lens andothers.

These optical elements are formed by injecting melted resins in a cavityof a molding die for molding a lens, in many cases. Hereafter, in thepresent specification, an optical element manufactured through injectionmolding employing a molding die is expressed as “a molded lens”.

With miniaturization of an optical pickup device in recent years, thereare disclosed various technologies about miniaturization of a moldedlens that constitutes an optical pickup device (see TOKKAI No.2002-243915 for example).

A molded lens described in TOKKAI No.2002-243915 is a lens having anouter form that is in a circular shape whose center is on an opticalaxis wherein outer circumference portions on the top and the bottom ofthe lens are cut off, and either one optical surface of both opticalsurfaces including the surface of incidence (first surface) and thesurface of emergence (second surface) is cut off and the other opticalsurface is not cut off, namely, an outer circumference of the otheroptical surface is kept to be in a circular form. By cutting off theouter circumference portions on the top and the bottom of the lens, alength (height) of the molded lens in the direction perpendicular to theoptical axis of the molded lens can be shortened, and miniaturization ofthe lens itself can be attained.

However, further miniaturization of the optical pickup device isdemanded in recent years, and there is caused a problem that a moldedlens which is smaller than the molded lens in TOKKAI No.2002-243915 isdemanded.

As shown in FIG. 4(a), on ordinary molded lens 100 having an outer shapein a circular form, there is provided bracket 102 for holding the lensat the position to cover the outer circumference of optical functionalsurface 101. The symbol 200 is a box-shaped cartridge for housingtherein a plurality of lenses 100, and on a part of left and right wallmembers 201, there is provided a vacant space 202 that extends in thelongitudinal direction (the direction perpendicular to the page). Then,by holding brackets 102 on both left and right sides in the vacant space202, a plurality of lenses 100 are housed in the longitudinal directionthe cartridge 200, in the structure.

On the molding die used for injection molding, there is usually provideda hole through which air in the cavity is driven out when melted resinsare injected in the cavity. Therefore, when melted resins entered a partof this hole are solidified when molding a lens, “a flash” which isprojected slightly from the surface is generally formed on the moldedlens.

Though this flash is sometimes projected in the radial direction fromthe outer circumference of the lens, it is hardly caused that flashes onadjoining two molded lenses 100 touch each other to be damaged, becauseeach lens 100 is rotatable freely on a horizontal plane crossing theoptical axis at right angles under the condition that the lens is heldin the vacant space 202, even when ordinary molded lenses 100 eachhaving a circular outer form are housed continuously in cartridge 200.

However, in the case of molded lens 300 whose outer circumferenceportion is cut out (see FIGS. 4(b) and 4(c)) such as one described inTOKKAI No. 2002-243915, a plurality of lenses 300 are held by causingthe cut out portion to touch a part of left and right wall members 201of the box-shaped cartridge.

In this case, when flash 301 (see FIG. 4(b)) is projected from an outercircumference (a portion other than a cut out portion) of lens 300, inthe radial direction, there has been a fear that flashes 301 on the twoadjoining molded lenses touch each other to be damaged, and a part ofthe damaged flash 301 is stuck on the optical surface of lens 300,because a movement of each lens 300 is regulated in a horizontal planethat crosses the optical axis at right angles by left and right wallmembers 201.

Further, there is an occasion where flash 301 is formed to be projectedin the optical axis direction from the surface of lens 300, and even inthis case, there is a problem of damage of flash 301 in the cartridge200, and there is a problem that positioning accuracy is worsened byflash 301 when flash 301 is formed on the surface (reference surface) onthe side used for positioning among both surfaces of lens 300, forexample.

SUMMARY OF THE INVENTION

An object of the invention is to provide a molded lens for an opticalpickup device wherein the aforementioned problems are taken intoconsideration, miniaturization is possible and an adverse effect causedby a flash can be controlled, and to provide a molding die for themolded lens.

The object mentioned above can be attained by either one of thefollowing Structures (1)-(10).

Structure (1) is a molded lens used in an optical pickup device in whicha plane of incidence having a first optical surface and a plane ofemergence having a second optical surface are provided, and a form of anouter circumference of the molded lens is formed by a first straightline portion which is in parallel substantially with a plane includingan optical axis, a second straight line portion which is in parallelwith the first straight line portion and is symmetric with the firststraight line portion about the above-mentioned plane and by twocircular arcs each connecting end portions of the first and secondstraight line portions, wherein a part of a fringe of each of the firstand second optical surfaces each being substantially in a form of acircle whose center is on the optical axis is cut off by each of thefirst and second straight line portions.

In the Structure (1), not only an outer circumference form but also thefirst and second optical surfaces are cut off by the first and secondstraight line portions, and thereby, the molded lens can beminiaturized.

Structure (2) is the molded lens described in Structure (1), whereinR1=R2 and 1>H/R1>2 are satisfied when radiuses of curvature of theaforementioned two circular arc portions are prescribed respectively asR1 and R2, and a distance between the first straight line portion andthe second straight line portion is prescribed as H.

In the Structure (2), the same effect as in Structure (1) is obtained,and miniaturization of a molded lens can be attained sufficiently bymaking a ratio (H/R1), in which H is the length of the portion which ismade to be shorter by cutting off a part of a substantially circularmolded lens having a radius R1 whose center is on an optical axis to theradius R1, to be small. However, if the ratio is established to be toosmall, the molded lens becomes longer in the direction perpendicular tothe optical axis, and there is a fear that melted resins cannot befilled completely in the cavity in the course of injection molding.

Structure (3) is a molded lens described in Structure (1), whereinR1=R2, 1>H1/R1>2 and |H1-H2|≧0.1 are satisfied when radiuses ofcurvature of the aforementioned two circular arc portions are prescribedrespectively as R1 and R2, a distance between peripheral portions of thefirst optical surface that is in a form of a circle whose center is onan optical axis and is cut off by the first straight portion and thesecond straight portion is prescribed as H1, and a distance betweenperipheral portions of the second optical surface that is in a form of acircle whose center is on an optical axis and is cut off by the firststraight portion and the second straight portion is prescribed as H2.

In the Structure (3), the same effect as in Structure (1) is obtained,and when a molding die (first molding die) for molding a portion of amolded lens including a plane of incidence and a molding die (secondmolding die) for molding a portion of the molded lens including a planeof emergence are united in the course of injection molding operations,it is possible to absorb a relative positional deviation caused betweenthe above-mentioned two molding dies, and thereby to improve workefficiency of injection molding operations, by making |H1-H2|≧0.1 tohold, namely, by making a difference between H1 and H2 to be 0.1 ormore.

Further, miniaturization of a molded lens can be attained sufficientlyby making a ratio (H1/R1), in which H1 is the length of the portionwhich is made to be shorter by cutting off a part of a substantiallycircular molded lens having a radius R1 whose center is on an opticalaxis to the radius R1, to be small. However, if the ratio is establishedto be too small, the molded lens becomes longer in the directionperpendicular to the optical axis, and there is a fear that meltedresins cannot be filled completely in the cavity in the course ofinjection molding.

Structure (4) is a molded lens used in an optical pickup device in whicha plane of incidence having a first optical surface and a plane ofemergence having a second optical surface are provided, and a form of anouter circumference of the molded lens is formed by a first straightline portion which is in parallel substantially with a plane includingan optical axis, a second straight line portion which is in parallelwith the first straight line portion and is symmetric with the firststraight line portion about the above-mentioned plane and by twocircular arcs each connecting end portions of the first and secondstraight line portions, wherein R1=R2 and 1<H/R1<2 are satisfied whenradiuses of curvature of the aforementioned two circular arc portionsare prescribed respectively as R1 and R2, and a distance between thefirst straight line portion and the second straight line portion isprescribed as H.

In the Structure (4), miniaturization of a molded lens can be attainedsufficiently by making a ratio (H/R1), in which H is the length of theportion which is made to be shorter by cutting off a part of asubstantially circular molded lens having a radius R1 whose center is onan optical axis to the radius R1, to be small. However, if the ratio isestablished to be too small, the molded lens becomes longer in thedirection perpendicular to the optical axis, and there is a fear thatmelted resins cannot be filled completely in the cavity in the course ofinjection molding.

Structure (5) is a molded lens used in an optical pickup device in whicha plane of incidence having a first optical surface and a plane ofemergence having a second optical surface are provided, and a form of anouter circumference of the molded lens is formed by a first straightline portion which is in parallel substantially with a plane includingan optical axis, a second straight line portion which is in parallelwith the first straight line portion and is symmetric with the firststraight line portion about the above-mentioned plane and by twocircular arcs each connecting end portions of the first and secondstraight line portions, wherein a flash that is caused when meltedresins enter an air vent port provided in a molding die cavity and aresolidified in the course of manufacturing the molded lens throughinjection molding is formed to be projected from a side of at least oneof the two circular arc portions, and the flash does not project from atangent line that passes through the point of intersection where animaginary straight line that passes through and crosses at right anglesan optical axis and extends in the direction which is in parallel withthe first and second straight line portions crosses the circular arcportion.

In the Structure (5), the flash does not project from a tangent linethat passes through the point of intersection where the imaginarystraight line that passes through the optical axis, intersects theoptical axis at right angles and extends in the direction that is inparallel with the first and second straight line portions crosses thecircular arc portion. Therefore, even in the case of holding a pluralityof molded lenses in a box-shaped cartridge by making the first andsecond straight line portions to touch a part of left and right wallmembers, adjoining two molded lenses touch each other on their circulararc portions, and it does not happen that a flash touches that of itsneighboring molded lens. It is therefore possible to prevent in advancethat flashes touch each other and a part of the damaged flash sticks toan optical surface of the molded lens.

Structure (6) is the molded lens described in Structure (5), wherein alength of the flash in the direction of an optical axis is 0.03 mm orless.

Structure (7) is the molded lens described in Structure (5) or Structure(6), wherein the flash is formed on a circular arc portion on one sideamong the two circular arc portions.

In the Structure (6) or (7), it is possible to prevent securely thatflashes touch each other.

Structure (8) is a molding die for molding a molded lens which isdescribed in either one of Structures (5)-(7), wherein a first moldingdie for molding a portion including a plane of incidence of the moldedlens and a second molding die for molding a portion including a plane ofemergence of the molded lens are provided, and the air vent port isformed on either one of the first and second molding dies.

In the Structure (8), the same effect as that of either one ofStructures (5)-(7) can be obtained.

Structure (9) is a molded lens for an optical pickup device equippedwith a plane of incidence having a first optical surface, a plane ofemergence having a second optical surface and with a flange portion thatcovers the fringe of the plane of incidence and that of the plane ofemergence, wherein either one of the surface of the flange portion onthe side of the plane of incidence and the surface of the flange portionon the side of the plane of emergence is made to be the referencesurface used for positioning a molded lens, the reference surface isformed to be projected from the plane of incidence or the plane ofemergence in the direction of an optical axis, a molded lens molding diefor manufacturing the molded lens is provided with a sleeve and a corethat moves in the direction of the optical axis relatively with thesleeve to push the molded lens out of the molding dye while it keepstouching the molded lens after injection molding, and a flash generatedwhen melted resins enter a vacant space that is formed on a contactportion between the sleeve and the core and are solidified, in thecourse of manufacturing the molded lens through injection molding,projects in the optical axis direction from the fringe of the plane ofincidence or the plane of emergence and does not project in the opticalaxis direction from the reference surface.

In the Structure (9), it is possible to prevent damage of a flash in acartridge in advance and to prevent the situation that positioningaccuracy for the molded lens is worsened by a flash formed on thereference surface.

Structure (10) is a molding die for molded lens for molding the moldedlens that is described in Structure (9), wherein a first molding die formolding a portion including a plane of incidence of the molded lens anda second molding die for molding a portion including a plane ofemergence of the molded lens are provided, and either one of the firstand second molding dies is composed of the sleeve and the core.

In the Structure (10), the same effect as that in Structure (9) can beobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are plan views of the primary portions showing aplane of incidence and a plane of emergence of a molded lens,respectively, in the first embodiment.

FIGS. 2(a) and 2(b) represent plan views of the primary portions showinga plane of incidence and a plane of emergence of a molded lens in thesecond embodiment, respectively, and FIG. 2(c) represents a side view ofprimary portions on the part of the plane of incidence.

FIGS. 3(a) represents a longitudinal section of primary portions of amolded lens and FIG. 3(b) is a longitudinal section of primary portionsof a molding die for molded lens both in the third embodiment.

FIG. 4(a) is a longitudinal section of primary portions of a cartridgefor holding a conventional circular molded lens, FIG. 4(b) is a planview for primary portions of a cartridge for holding a molded lens whoseone portion is cut off, and FIG. 4(c) is a longitudinal section forprimary portions of the cartridge.

DETAILED DESCRIPTION

(First Embodiment)

An embodiment of the molded lens of the invention will be explained asfollows, referring to the drawings.

Incidentally, in each drawing, let it be assumed that x represents adirection of optical axis L of the molded lens, y represents a directionthat is perpendicular to the optical axis L and z represents a directionperpendicular to the direction X and the direction y.

As shown in FIGS. 1(a) and 1(b), molded lens 10 is provided with planeof incidence 20, plane of emergence 30 and flange portion 40.

Further, among optical surfaces of the molded lens 10, it is assumedthat an optical surface on the part of the plane of incidence 20 isfirst optical surface 21, while an optical surface on the part of theplane of emergence 30 is second optical surface 31.

An outer circumference of the molded lens 10 is formed by first straightline portion 11 which is in parallel substantially with a plane (X—Zplane) including optical axis L, second straight line portion 12 whichis in parallel with the first straight line portion 11 and is symmetricwith the first straight line portion 11 about the plane includingoptical axis L and by two circular arc portions 13 and 14 eachconnecting end portions of the first and second straight line portions11 and 12. As stated above, the outer circumference of the molded lens10 is in a shape that is formed by cutting off a mostly circular formhaving its center on optical axis L with the first and second straightline portions 11 and 12.

Further, on the part of the plane of incidence 20, a part of the fringeof mostly circular first optical surface 21 having its center on opticalaxis L is cut off by the first and second straight line portions 11 and12, and on the part of the plane of emergence 30, a part of the fringeof mostly circular second optical surface 31 having its center onoptical axis L is cut off by the first and second straight line portions11 and 12.

As stated above, with respect to the molded lens 10 of the invention,not only its outer circumference form is cut off by the first and secondstraight line portions, but also the first and second optical surfaces21 and 31 are cut off by the first and second straight line portions,and thereby, the molded lens can further be miniaturized.

Incidentally, a light flux arrives at a cutout portion of the firstoptical surface 21 among light fluxes emitted from a light source andarrive at the plane of incidence 20 does not emerge from the secondoptical surface 31 of the plane of emergence 30 and does not form alight-converged spot on an information recording surface of an opticalinformation recording medium. Ordinarily, however, all light fluxesemitted from a light source do not always form a light-converged spot,and for example, light fluxes passing through an area other than thosewith the necessary numerical aperture are intercepted by a diaphragmarranged in the vicinity of a plane of incidence of an objective lens.Therefore, even if the light flux arrives at a cutout portion of thefirst optical surface 21 is not utilized for forming a light-convergedspot as stated above, the efficiency of an optical pickup device is notworsened. Incidentally, a distance between the first straight lineportion 11 and the second straight line portion 12 is adjustedappropriately by a design based on a type of the optical informationrecording medium in which the optical pickup device is used and on awavelength of the light flux.

It is preferable to design a lens so that R1=R2, 1<H1/R1<2 and|H1−H2|≧0.1 are satisfied under the assumption that R1 and R2 representrespectively radiuses of curvature of two circular arc portions 13 and14, H1 represents a width of a portion cut off by the first straightline portion 11 and the second straight line portion 12 on a fringeportion of a mostly circular first optical surface 21 having its centeron optical axis L, and H2 represents a width of a portion cut off by thefirst straight line portion 11 and the second straight line portion 12on a fringe portion of a mostly circular second optical surface 31having its center on optical axis L.

By making a ratio (H1/R1), in which H1 is the length of the portionwhich is made to be shorter by cutting off a part of a substantiallycircular molded lens 10 having a radius R1 whose center is on opticalaxis L to the radius R1, to be smaller than 2, miniaturization of moldedlens 10 can be attained sufficiently, and by making the ratio to begreater than 1, it is possible to prevent the molded lens 10 frombecoming excessively long in the Z direction. If the ratio H1/R1 isestablished to be smaller than 1, there is a fear that the molded lens10 becomes longer in the Z direction, and melted resins cannot be filledcompletely in the cavity in the course of injection molding.

Further, by making |H1-H2|>0.1 to hold, namely, by making a differencebetween H1 and H2 to be 0.1 or more, when a molding die (first moldingdie) for molding a portion including plane of incidence 20 of moldedlens 10 and a molding die (second molding die) for molding a portionincluding plane of emergence 30 of the molded lens 10 are united in thecourse of injection molding operations, it is possible to absorb arelative positional deviation caused between the above-mentioned twomolding dies, and thereby to improve work efficiency of injectionmolding operations.

Incidentally, it is also possible to design a lens so that R1=R2 and1<H1/R1<2 may be satisfied under the condition of H1=H2.

Further, the molded lens 10 shown in the present embodiment can be usedpreferably for a collimator, a coupling lens, a correction plate and anobjective lens having a relatively small image-side numerical aperture(NA is about 0.45), for example, which constitute an optical pickupdevice.

(Second Embodiment)

An embodiment of the molded lens 10 and a molding die for the moldedlens relating to the invention will be explained as follows, referringto FIGS. 2(a)-2(c).

In the same way as in the molded lens 10 of the First Embodimentmentioned above, an outer peripheral shape of molded lens 10 in thepresent embodiment is formed by first straight line portion 11, secondstraight line portion 12 and two circular arc portions 13 and 14.Incidentally, flange portion 40 is formed on the position that coversperipheries of plane of incidence 20 and plane of emergence 30.

A part of a fringe for each of first optical surface 21 and secondoptical surface 31 each being substantially in a circular form havingits center on optical axis L is cut off by the first and second straightline portions 11 and 12. Incidentally, in the molded lens 10 in thepresent embodiment, a part of a fringe of an optical surface on at leastone of the first optical surface 21 and the second optical surface 31has only to be cut off by the first and second straight line portions 11and 12.

A flash that is caused when melted resins enter an air vent portprovided in a molding die cavity and are solidified in the course ofmanufacturing the molded lens 10 through injection molding is formed tobe projected from two portions on a side of one circular arc portionamong two circular are portions 13 and 14. Incidentally, detailedexplanation for flash 50 will be omitted here because is widely known.

Each flash 50 is provided not to project from tangent line L2 thatpasses through the point of intersection where imaginary straight lineL1 (straight line that passes through optical axis L and extends in theZ direction) crossing optical axis L at right angles crosses circulararc portions 13 and 14.

Even in the case of holding a plurality of molded lenses in a box-shapedcartridge by making the first and second straight line portions to toucha part of left and right wall members, adjoining two molded lenses 10touch each other on their circular arc portions 13 and 14, and it doesnot happen that a flash 50 touches the neighboring flash, by providingflash 50 as stated above. It is therefore possible to prevent in advancethat a part of the damaged flash 50 caused by mutual touching of flashes50 is stuck on the optical surface of the molded lens 10.

Incidentally, it is preferable that a length of flash 50 in thedirection of optical axis L is made to be 0.03 mm or less, and the flashis provided on a circular portion of one of two circular portions 13 and14. By providing flash 50 to satisfy the aforesaid condition, it ispossible to prevent surely the mutual touching of flashes 50.

For molding the molded lens 10 having the flash 50 mentioned above, anair vent port has only to be provided in a cavity of either one moldingdie among the first molding die for molding a portion including plane ofincidence 20 of molded lens 10 and the second molding die for molding aportion including plane of emergence 30 of molded lens 10, bothconstituting a molding die (molding die for molded lens).

Incidentally, the molded lens 10 shown in the present embodiment can beused preferably for a collimator and an objective lens which constitutean optical pickup device.

(Third Embodiment)

Next, an embodiment of the molded lens 10 and molding die for the moldedlens 60 relating to the invention will be explained as follows.

In the same way as in the molded lens 10 of the Second Embodimentmentioned above (refer to FIGS. 2(a) to 2(c)), an outer peripheral shapeof the molded lens 10 in the present embodiment is formed by firststraight line portion 11, second straight line portion 12 and twocircular arc portions 13 and 14. Further, a part of a fringe for each offirst optical surface 21 and second optical surface 31 each beingsubstantially in a circular form having its center on optical axis L iscut off by the first and second straight line portions 11 and 12.Incidentally, in the molded lens 10 in the present embodiment, a part ofa fringe of the first optical surface 21 and the second optical surface31 does not need to be cut off by the first and second straight lineportions 11 and 12, and the molded lens may also be molded lens 10having an outer form that is substantially in a circular form having itscenter on optical axis L which is used generally.

Further, flange portion 40 is formed on the position that coversperipheries of plane of incidence 20 and plane of emergence 30.

As shown in FIG. 3(a), either one (surface 41 on the plane of incidenceside in the present embodiment) of surface 41 on the plane of incidenceside of flange portion 40 and surface 42 on the plane of emergence sideis made to be reference surface K for positioning the molded lens 10.

The reference surface K is formed to project from the plane of incidence20 in the direction of optical axis L.

As shown in FIG. 3(b), first molding die 61 for molding a portionincluding plane of incidence 20 of molded lens 10 is composed of sleeve61 a and core 61 b that pushes the molded lens 10 out of the molding dieby moving relatively to the sleeve 61 a in the direction of optical axisL, while touching the plane of incidence 20 of molded lens 10 afterinjection molding.

Molding die for molded lens 60 is composed of the first molding die 61and second molding die 62 for molding a portion including plane ofemergence 30 of molded lens 10.

Ordinarily, for moving (sliding) the core 61 b smoothly, there isprovided vacant space 63 on a contact portion between the upper endportion of an inner circumferential surface of the sleeve 61 a and theupper end portion of an outer circumferential surface of the core 61 b.

Further, this vacant space 63 is used not only for securing slidingproperty of the core 61 b but also for air vent in the case of injectionof melted resins in a cavity of the molding die.

Therefore, by adjusting a length of the vacant space 63 in the directionof optical axis L, it is possible to provide the flash 50 that is causedwhen melted resins enter the vacant space 63 and are solidified, so thatthe flash may project from a periphery of the plane of incidence 20 inthe direction of optical axis L and may not project from the referencesurface K in the direction of optical axis L.

Due to this, it is possible to prevent damage of flash 50 in a cartridgein advance, for example, and to prevent the situation that positioningaccuracy for the molded lens 10 is worsened by a flash 50 formed on thereference surface.

Incidentally, the molded lens 10 shown in the present embodiment can beused preferably for a collimator, a coupling lens, a correction plateand an objective lens, for example, which constitute an optical pickupdevice.

The invention makes miniaturization of a molded lens to be possible, andprevents damage of a flash and a change for the worse of positioningaccuracy caused by the flash.

1. A molded lens for use in an optical pickup device, said molded lenscomprising: (a) a plane of incidence including a first optical surface;(b) a plane of emergence including a second optical surface provided onan opposite side of the molded lens with respect to the plane ofincidence; and (c) an outer circumference surface having a shape formedby: (i) a first straight line portion which is substantially parallel toa plane including an optical axis of the molded lens, (ii) a secondstraight line portion which is substantially parallel with the firststraight line portion is symmetric with the first straight line portionabout the plane including the optical axis of the molded lens, and (iii)two circular arcs each connecting end portions of the first and secondstraight line portions; wherein each of the first and second opticalsurfaces has a shape substantially corresponding to a respective circlehaving a center on the optical axis and having outer portions thereofcut off by the respective first and second straight line portions; andwherein the following numerical expressions are satisfied:R 1=R 2 and 1<H/R 1<2 where R1 and R2 represent respective radiuses ofcurvature of the two circular arc portions, and H represents a distancebetween the first straight line portion and the second straight lineportion.
 2. A molded lens, for use in an optical pickup device, saidmolded lens comprising: (a) a plane of incidence including a firstoptical surface; (b) a plane of emergence including a second opticalsurface provided on an opposite side of the molded lens with respect tothe plane of incidence; and (c) an outer circumference surface having ashape formed by: (i) a first straight line portion which issubstantially parallel to a plane including an optical axis of themolded lens, (ii) a second straight line portion which is substantiallyparallel with the first straight line portion and is symmetric with thefirst straight line portion about the plane including the optical axisof the molded lens, and (iii) two circular arcs each connecting endportions of the first and second straight line portions; wherein each ofthe first and second optical surfaces has a shape substantiallycorresponding to a respective circle having a center on the optical axisand having fringe portions thereof cut off by the respective first andsecond straight line portions; and wherein the following numericalexpressions are satisfiedR 1=R 2, 1<H 1/R 1 <2 and |H 1-H 2|≧0.1 where R1 and R2 representrespective radiuses of curvature of the two circular arc portions, H1represents a distance between the fringe portions of the first opticalsurface, and H2 represents a distance between the fringe portions of thesecond optical surface.
 3. A molded lens for use in an optical pickupdevice, said molded lens comprising: (a) a plane of incidence includinga first optical surface; (b) a plane of emergence including a secondoptical surface provided on an opposite side of the molded lens withrespect to the plane of incidence; and (c) an outer circumferencesurface having a shape formed by: (i) a first straight line portionwhich is substantially parallel to a plane including an optical axis ofthe molded lens, (ii) a second straight line portion which issubstantially parallel to the first straight line portion and issymmetric with the first straight line portion about the plane includingthe optical axis of the molded lens, and (iii) by two circular arcs eachconnecting end portions of the first and second straight line portions;wherein the following numerical expressions are satisfied:R 1=R 2 and 1<H/R 1<2 where R1 and R2 represent respective radiuses ofcurvature of the two circular arc portions, and H represents a distancebetween the first straight line portion and the second straight lineportion.